The present invention pertains to wafer level test and wafer level test and burn-in devices employing a large array of spring contacts held against the wafer undergoing test and/or burn-in.
Electrical testing of semi-conductor wafers wherein all the devices in the wafer are tested simultaneously is of considerable interest to the semiconductor industry. At present, the testing of integrated circuit chips in wafer form is limited in scope or tends to be a slow procedure permitting only testing of a few chips at a time. That is, wafer testing is often performed using a mechanical stepping device with few chips (e.g. 1 to 32) tested at a time.
Further, current testing methods do not lend themselves to accelerating failure testing procedures, such as burn-in. A certain percentage of the integrated circuits (ICs) fail in the first few hours or days of use. Under current practice such devices are first packaged and then burnt-in in module form or burnt-in in a single diced chip form. Due to a lack of the necessary wafer level contacting system in industry, no wafer level test or burn-in systems are available. Test and burn-in at the wafer level is the least expensive manufacturing method and is thus highly desired.
An example of a wafer level test and burn-in arrangement is shown in International Patent Application No. PCT/US92/07045 wherein Applicants utilize solder bumps on the test head to contact the full wafer. One disadvantage of this method and apparatus is the extreme force required to make good contact with the wafer. Also, solder deforms permanently after each test, thus requiring reflow of solder on the test fixture after each use.
Another approach is shown in International Application No. PCT/US95/14843 wherein a wafer contact system is made of shaped gold wires and coated with a hard metal (e.g. nickel) to impart desired spring characteristics to the device. A big disadvantage of this approach is that the spring contact will deform permanently if the product wafer and the test head surface are not substantially flat. Due to the fact that extreme planarity in current manufacturing processes can not be assured, this method can not be used for wafer level test and burn-in.
U.S. Pat. No. 4,993,957 discloses replacing the metal contact with a filled polymer ball or cylinder to reduce contact damage during the testing of microelectric devices.
U.S. Pat. No. 5,367,254 describes a buckling beam probe biased to a higher order buckling by lateral slots, thus allowing more travel without increasing lateral deformation.
U.S. Pat. No. 5,389,885 discloses a device with an array of traditional spring contacts replaced by loose pins which are backed by a common diaphragm which provides preload and spring compliance.
U.S. Pat. No. 5,089,305 discloses and claims a manufacturing method wherein stacks of printed wiring boards are interconnected by their respective through-holes by stretching and threading a memory metal through the holes, then raising the temperature to return the wire to its memorized crimped shape. The crimping action puts the wire into intimate contact with the barrel of each through-hole in the stack.
U.S. Pat. No. 4,639,060 discloses making connection to an insulated wire without having to strip the insulation. The connector consists of an aperture which closes by use of a memory-alloy returning to memorized shape when the temperature is raised and thus the insulation is pierced.
Japanese Published Patent Application 60/28583 describes a ZIF socket used to mount an integrated circuit wherein shape-memory alloys are used.
Japanese Patent Application 63/02255 discloses using a shape memory alloy for moving a contact pin in a test fixture for microelectric devices.
Spring contacts used in a microelectronic wafer test and/or wafer level test and burn-in apparatus are fabricated from a shape memory metal, the shape memory metal plastically deforming under normal test or burn-in contact loading, the metal, in one embodiment, having a transition temperature at or above the burn-in temperature. According to the present invention spring contacts constructed from a shape memory alloy can readily deform to make the necessary contact during the test procedure. Upon retraction from the testing procedure or position the contacts can be heated to their transition temperature and the original shape of the spring contacts is thereby restored.
A preferred shape memory alloy for use in the invention is an alloy of 42 to 48% by weight titanium balance nickel.
Spring contacts can be formed on a composite structure by using a shape memory metal spring attached to a standard spring made of a conventional spring metal such as beryllium copper or phosphor bronze.
In another embodiment of the invention the shape-memory is selected from those metals or alloys that would plastically deform during cool-down after burn-in and have a transition temperature at or below the burn-in temperature.
In any embodiment of the invention the spring metal can be coated with gold or other contact material in the vicinity of the spring that would contact the part undergoing test.
Thus in one embodiment of the invention a semi-conductor wafer test and/or burn-in spring contact is either a shape memory metal, the metal plastically deforming under normal test or burn-in contact loading and having a transition temperature at or above the burn-in temperature or the shape memory metal in combination with another metal.
In another embodiment of the invention a spring contact for a microelectronic test or burn-in device is either a shape memory metal plastically deforming under normal test or burn-in contact loading, the metal having a transition temperature at or above the burn-in temperature or the shape memory metal in combination with another metal.
In yet another embodiment the invention a semi-conductor wafer test and/or burn-in spring contact is either a shape memory metal, the metal plastically deforming under normal test or burn-in contact loading and having a transition temperature at or below the burn-in temperature or the shape memory metal in combination with another spring metal.
A further embodiment of the invention is a spring contact for a microelectric test or burn-in device in either a shape memory alloy that plastically deforms under normal test or burn-in contact loading and has a transition temperature at or below the burn-in temperature or is a shape memory metal in combination with another metal.
The present invention also includes a method of improving a semi-conductor wafer test and/or burn-in apparatus utilizing spring contacts by the step of replacing the spring contact with either a shape memory metal or the shape memory metal and another metal, the shape memory metal selected from the group consisting of a shape memory alloy that plastically deforms under test or burn-in conditions and has a transition temperature at or above the burn-in temperature and a shape memory metal that plastically deforms under test or burn-in conditions and has a transition temperature at or below the burn-in temperature.